Graphite foam material and method of making same

ABSTRACT

Methods of making a graphite material are provided. A flexible graphite is ground into a powder. The graphite powder is mixed with a resin and the mixture is hot pressed. A second method of making a graphite material is provided where the graphite is ground into a powder; the graphite powder is soaked in a cryogenic liquid; the soaked graphite powder is then expanded; the expanded soaked graphite powder is mixed with a graphite powder; and the graphite powder mixed with a resin are hot pressed. According to a third method, the flexible graphite is ground into a powder; the graphite powder is soaked into a cryogenic liquid, the soaked graphite powder is expanded; and the expanded soaked graphic powder is ground into a fine powder. The resulting graphite powder is mixed with a resin. The graphite powder mixed with the resin is hot pressed. According to a fourth method, graphite flakes are soaked into an acid; the soaked graphite flakes are expanded; and the expanded soaked graphite flakes are precompacted. The precompacted soaked graphite flakes are ground into a powder. The ground precompacted expanded soaked graphite powder is then mixed with a resin. The graphite powder with the resin is hot pressed.

[0001] This is a continuation of U.S. patent application Ser. No.08/724,177 filed Sep. 30, 1996, which is a continuation of U.S. patentapplication Ser. No. 08/591,363 filed Jan. 25, 1996.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to graphite foam material, of the type usedfor high temperature insulation and the like, and to a method of makingthe same. The invention also relates to a graphite material that may beused and added to provide protection from electrostatic discharge (ESD)or shielding from electromagnetic and radio interference (EMI/RFI).

[0004] 2. Art Background

[0005] In the prior art, various forms of graphite material have beenused as insulating materials in high temperature applications includingindustrial ovens and furnaces, vacuum furnaces and controlled atmosphereheating apparatus and the like.

[0006] One of the first such graphite insulating materials was powderedcarbon black which had an appropriate amount of insulating capacity, butwas very difficult to handle, relatively heavy, and extremely timeconsuming to replace. As a result with the advent of foam and resinchemistry, a number of newer materials were developed which were lighterand easier to handle, but which had the requisite insulating capacity.One such material is a carbon fiber insulating material made of a carbonfiber held in a matrix by a phenolic resin material, and formed into aboard or block.

[0007] Static electricity and electrostatic discharge (ESD) arenaturally occurring phenomena. Simply stated, static electricity iselectrical energy at rest on a surface. It is generally created by therubbing together and separating of two materials, one of which isusually non-conductive. Typically, one material gives up electrons andbecomes positively charged; the other takes on the electrons and becomesnegatively charged. ESD may be defined as the sudden discharge of anelectrostatic potential from one body to another. A good example may bethe shock one receives when touching a metal door knob after walkingacross a carpeted floor.

[0008] In many environments, ESD may damage or destroy sensitiveelectronic components, erase or alter magnetic media, or set offexplosions or fires in flammable environments. These discharges may becaused by a variety of sources, most commonly there is a directdischarge from a person or equipment into a sensitive object.

[0009] One way of preventing ESD is to reduce the generation of chargesin the first place. A second way of preventing ESD is to provide aground path for the safe dissipation of accumulated charges to ground. Athird method is to provide shielding or protection of devices andequipment from discharge through packaging. ESD may also be controlledwith materials, such as conductive plastics, that do not generate highlevels of charge, that dissipate charges before they accumulate todangerous levels, or that provide electrostatic shielding to preventcharges from reaching the sensitive product.

[0010] Electromagnetic Interference (EMI) is electrical energy, eitherelectromagnetic or in the radio frequency (RF) range in the case ofradio frequency interference (RFI) that is radiated by specific sources.Some of these sources include computer circuits, radio transmitters,fluorescent lamps, color TV oscillators, electric motors, automotiveignition coils, overhead power lines, lightning, TV games, and manyother resources. EMI/RFI may interfere with the operation of simplehousehold appliances such as causing the unwanted operation of garagedoor openers. On another level, EMI/RFI may corrupt data in large scalecomputer systems, cause inaccurate readings and output in aircraftguidance systems, and interrupt the functioning of medical devices, suchas pacemakers.

[0011] Proper shielding may prevent products from emittingelectromagnetic or radio frequency energy to other susceptibleequipment. Shielding may also protect susceptible equipment from theeffects of externally radiated EMI/RFI as the shielding absorbs theenergy emitted, converting it to thermal energy.

[0012] EMI thermoplastic composites are used primarily for shieldingagainst emission or reception of EMI and RFI. Traditionally, shieldinghas been accomplished by encasing sensitive electronic parts in metalhousings or by using metallic coatings on the inside of plastichousings. Thermoplastic compounds with appropriate shielding additivesare cost effective alternatives in many applications due to theirability to take on complex shapes and maintain tight tolerances.

[0013] It is desirable to provide, at relatively low cost, a compound/sthat may dissipate charges before they accumulate to dangerous levels,that provide electrostatic shielding to prevent charges from reachingthe sensitive product. Moreover, it is desirable to provide, atrelatively low cost, a material for shielding against emission orre-emission of electrostatic.

SUMMARY OF THE INVENTION

[0014] The present invention is a composition of matter, andspecifically, a material comprising cryogenically treated graphite orcarbon particles which are then expanded by thermal shock/gas expansion.The expanded particles are then combined with a phenolic resin, or thelike, and then thermoset under pressure at an elevated temperature toform a hardened sheet or plate. The carbon or graphite particles can beobtained from previously expanded graphite which has been made intoflexible graphite foil, and therefore, the present invention permits therecycling of graphite foil which is not otherwise commerciallydistributed. The method of making said material is also described andclaimed.

[0015] The material has generally the same insulating and other physicalcharacteristic as the prior art carbon fiber insulation materials, andit is less expensive than prior art materials.

[0016] Another advantage of the present invention is that it canutilize, without any drawbacks, recycled flexible graphite material, asa starting material. Such recycled flexible graphite material iscurrently typically being landfilled. Thus, the present invention isparticularly advantageous as a benefit to the environment. Additionally,the advantageous method of making the material and the quality of thematerial made in accordance with the present invention provideadditional benefits.

[0017] Another advantage is the reduced weight loss due to oxidation,resulting in longer furnace life between successive rebuilding of thefurnace.

[0018] According to the present invention, one may use finished lowdensity blocks, boards, billets, etc. to make higher density parts bycutting (i.e., using, for example, a cork bore or saw) to shape or moldthe material into a desired shape and pressing using different pressuresto the obtain desired density. For example, die formed rings can be madeusing the present invention. The compressive strength of the die formedrings was greater than or equal to the strength of some monolithicgraphites of the prior art.

[0019] The present invention also includes a graphite material and amethod for making the graphite material by using a thermoplasticmaterial mixed with re-expanded graphite. The compound of thermo plasticmaterial and re-expanded graphite is fed into an injection moldingsystem at a relatively high temperature and injected into a mold where aplastic material is formed. The plastic material is then removed fromthe mold when the material is still very hot but hard set.

[0020] The present invention further includes in one embodiment thereofa method of making a graphite material. Flexible graphite is ground intoa powder having a particle size in the approximate range of 25 to 80mesh. The graphite powder is mixed in an amount ranging betweenapproximately 10% - 90% graphite powder by weight, with a resin, in anamount ranging between approximately 10% - 90% by weight. The graphitepowder, mixed with the resin is hot pressed.

[0021] The present invention also provides in another embodiment thereofa method of making a graphite material. A flexible graphite is groundinto a powder having a particle size in an approximate range of 25 - 80mesh. The graphite powder is soaked in a cryogenic liquid. The soakedgraphite powder is expanded. The resulting graphite powder is mixed inan amount ranging between approximately 10% - 90% by weight with aresin, in an amount ranging between approximately 10% - 90% by weight.The expanded soaked graphite powder that has been mixed with the resinis then hot pressed.

[0022] The present invention further provides in another embodimentthereof a method of making a graphite material. A flexible graphite isground into a powder having a particle size in an approximate range of25 - 80 mesh. The graphite powder is then soaked in a cryogenic liquid.The soaked graphite powder is then expanded. The expanded soakedgraphite powder is ground into a powder having a particle size in anapproximate range of 48 to 100 mesh. The resulting graphite powder ismixed, in an amount ranging between approximately 10% - 90% by weightwith a resin in an amount ranging between approximately 10% - 90% byweight. The graphite powder mixed with the resin is then hot pressed.

[0023] The present invention provides in another embodiment thereof amethod of making a graphite material. Initially, graphite flakes aresoaked in an acid. The soaked graphite flakes are then expanded. Thesoaked expanded graphite flakes are precompacted. The precompactedexpanded soaked graphite is then ground into a powder that has aparticle size in a range of approximately 25 to 80 mesh. The graphitepowder is mixed an amount ranging between approximately 10% - 90% byweight with a resin in an amount ranging between approximately 10% - 90%by weight. The graphite powder that has been mixed with the resin isthen hot pressed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The objects, features and advantages of the present inventionwill become apparent to one skilled in the art from reading thefollowing detailed description in which:

[0025]FIG. 1 is a flow chart showing on embodiment of process of thepresent invention;

[0026]FIG. 2 is a schematic drawing of the heat shock apparatus used inone method of the present invention;

[0027]FIG. 3 is a graph showing the oxidation weight loss of prior artrigid felt as compared with the material of the present invention, whichis the invented material at 670° C. over time;

[0028]FIG. 4 is a graph showing the final density of the inventedmaterial as a result of the compressive force applied to it;

[0029]FIG. 5 is a graph showing steps of a second embodiment of a methodaccording to the present invention;

[0030]FIG. 6 is a flow chart diagram illustrating a third embodiment ofa process of making a graphite material according to the presentinvention;

[0031]FIG. 7 is a flow chart diagram illustrating a fourth embodiment ofa process of making a graphite material according to the presentinvention;

[0032]FIG. 8 is a flow chart diagram illustrating a fifth embodiment ofa process of making a graphite material according to the presentinvention;

[0033]FIG. 9 is a flow chart diagram illustrating a sixth embodiment ofa process of making a graphite material according to the presentinvention; and

[0034]FIG. 10 illustrates a graph in connection with the resistivity permeter square of the graphite material produced by way of the third,fourth, fifth and sixth embodiments of the method of making a graphitematerial according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] In the following description, numerous specific details are setforth to provide a thorough understanding of the present invention.However, one having ordinary skill in the art should recognize that theinvention may be practiced without these specific details. In someinstances, well-known circuits, structures, and techniques have not beenshown in detail to avoid obscuring the present invention.

[0036] The present invention relates to a material and methods of makingmaterials, with different densities, the materials having superior heatinsulation capacity for use in furnaces and other apparatus. The methodof making the present invention is shown in the flow chart in FIG. 1.

[0037] The starting material is preferably recycled flexible graphite,such as the type which may be obtained as a byproduct from themanufacture of flexible graphite rolls.

[0038] The flexible graphite material is sometimes referred to asvermiculated graphite. It is a graphite material which has already beensubjected to an expansion process, typically an acid treatment ofgraphite followed by a heat shock treatment. The starting material canbe in the form of chunks, bricks, strips, or any other form which may beobtained.

[0039] The flexible graphite is first ground to a very fine powderhaving a particle size in the range of 35 to 80 mesh and a tap densityof approximately 0.177 - 0.230 g/cc. Somewhat smaller or larger mesh canbe used as well, but the particle size is preferably within the range of35 to 80 mesh as specified. The flexible graphite can be ground in acone mill grinder or hammer mill grinder or other grinder known in theart.

[0040] In the next step, the powdered carbon particles are poured into acontainer of liquid nitrogen, and permitted to absorb sufficient liquidnitrogen so that they sink in the container below the surface of theliquid nitrogen. It is believed that other cryogenic liquids may alsowork, and are deemed to be within the scope of the present invention.The sinking of the particles, while not deemed critical to the subjectprocess, appears to be an adequate indicator of sufficient absorption ofthe liquid nitrogen into the particles, which is important in thefollowing expansion step.

[0041] Alternatively, one may treat ground flexible graphite with acidsuch as fuming nitric acid, sulfuric acid, etc., and then heat thecompound, of the respective acid and ground flexible graphite, therebycausing graphite to expand. For example, an experiment was conductedusing 4 grams of ground flexible graphite and 6 centimeters cube (cc) offuming nitric acid. The compound was then heated to 1100° Celsius (C.).The expansion ratio obtained was 8 to 10 times.

[0042] The liquid nitrogen soaked carbon particles or the groundflexible graphite particles treated with one of the above-mentionedacids are next injected into a hot air burner in an oven with an airstream flowing therethrough, the oven temperature being approximately650° Fahrenheit (F.). One such acceptable hot air burner is a propaneburner such as a Universal® 40,000 BTU per hour propane heater. Onepossible arrangement is shown in FIG. 2. As shown the heat shock/gasexpansion apparatus comprises a propane heater 20, with the heated airflow direction shown by arrow A, coupled through a conduit 22 to areceiving means 24 which receives the liquid nitrogen soaked particlesthrough the top inlet 26 (which are added in the direction shown byarrow B. The receiving means 24 is coupled through conduit 26 to heattreated particles receiving means 28, which has a screen 30 to preventthe particles, which are now very light, from becoming excessivelyairborne.

[0043] If the recycled graphite particles are used, this heat treatmentor thermal shock/gas expansion expands the particles to about 4 to 8times their original size, and the density of the particles is in therange of 0.080 to 0.030 grams per cubic centimeter. The expandedparticles may be compressed and molded to the desired size, shape anddensity without using the next steps.

[0044] The expanded, thermally-shocked, carbon material is then mixedwith a resin, and preferably a phenolic resin, and most preferably aphenolic resin such as Borden Durite RD-2414 in a preferred ratio ofabout 60% carbon to 40% resin by weight. Other ratios may be used, andthe selection of a ratio is within the skill of persons of ordinaryskill in the art.

[0045] The mixture is then thermoset at a temperature of 350° F. and apressure dependent upon the density required for about 1 hour. The shapeof the product can be any shape and size as required for the intendedpurpose.

[0046] The thermoset product is then heat treated in a furnace. Thetemperature of the heat treatment is preferably about 2000° F., but mayvary from 1000 - 5000° F. depending upon final usage.

[0047] The density may be in the range from less than 0.1 g/cc toapproximately theoretical density.

[0048]FIG. 3 shows a comparison of prior art material to the material ofthe present invention, and particularly shows that there issubstantially more weight loss from the prior art material being exposedto elevated temperature over time which is considered disadvantageous tothose skilled in the art.

[0049]FIG. 4 illustrates the density of the material as a result of thepressure applied to it during its manufacture.

[0050] In another embodiment of the present invention, a method formaking a substantially high density graphite material with plasticcharacteristics (graphite-plastic) is provided. The main steps of thismethod are shown in FIG. 5. According to this method, a thermoplasticmaterial, such Polyphelene Sulfide (PPS) may be mixed with re-expandedgraphite thereby producing graphite pellets. The pellets may then beexpanded by using the expansion process described in the foregoing. Inthis respect, the description of the expansion process presented in theforegoing is herein incorporated by reference. Note that while theexpansion process is not necessary to the method described herein, thisprocess is, however, preferable.

[0051] In the embodiment, of the method according to the presentinvention, described herein, the compound material, i.e., pellets,include a thermoplastic material mixed with 45-60% re-expanded graphite,but the present invention is not limited in scope in this respect. Thecompound material is then injected into a mold at a temperature ofapproximately 650° F. The mold may have an approximate dimension of6″×9″×0.125″, but the present invention is not limited in scope in thisrespect. The injection of the compound may be performed forapproximately 1 minute. Graphite material with plastic characteristicsis then formed into plates, or other type of shapes in the mold at atemperature of 250° Fahrenheit and removed therefrom when the materialis still hot, but hard set.

[0052] The resulting graphite material with plastic characteristicsproduced may be formed into different geometry's due to its high densityof the produced which allows the graphite-plastic materials produced tobe shaped better. The graphite-plastic plates obtained have a density ofapproximately 1.5 grams per cc. It is believed that any thermoplasticmaterial may be used in this process instead of the PPS.

[0053] A graphite-plastic material according to the present inventionmay also be obtained by using a thermosetting plastic such as phenolicresin, epoxy resin, and mixing it with graphite powder. The compound ofthermoset material and the graphite powder may then be heated to atemperature that is below the thermosetting temperature (350° F.) forapproximately an hour and then introduced in a mold by using a processof hot pressing which is well-known by one skilled in the art. It willbe noted that instead of graphite powder, re-expanded graphite may beused in this process.

[0054] The present invention also provides a method for making anelectrically conductive plastic that has a relatively low resistivity.According to this process, a PPS material or a liquid crystal polymer(LCP) resin is mixed with re-expanded graphite to make pellets asexplained above. The pellets are then mixed in a tumbler with 20% byweight nickel coated carbon fibers. The nickel coated carbon fibers maybe a mixture of 50% carbon particles and 50% nickel in variousconcentrations. The addition of nickel coated carbon fibers to thepellets causes a decrease the bulk resistance of the pellets fromapproximately 0.100 ohm inches to 0.00085 ohm inches. Then this compoundis subject to an injection molding process as explained in theforegoing. The material produced has both a low electrical resistivityand a high corrosion resistance. Moreover, the material produced may beused for bipolar plates in photon exchange membrane (PEM) type fuelcells, gaskets such as intake manifold, flange gaskets, etc. forautomotive devices.

[0055]FIG. 6 illustrates a flow chart diagram for a third embodiment ofa process of making a graphite material according to the presentinvention. The process starts at step 602 where flexible graphite isground into a very fine powder having a particle size in an approximaterange of 25 - 80 mesh and a tap density in a range of approximately0.177 - 0.230 grams/centimeter cube (g/cc). However, the presentinvention may be practiced in connection with other particle sizes andtap densities. The flexible graphite may be ground in a cone millgrinder or hammer mill grinder or other grinder known in the art. In oneembodiment, the starting material may be recycled flexible graphite, ofa type which may be obtained as a byproduct from the manufacture offlexible graphite rolls. The starting material may be in the form ofchunks, bricks, strips, or any other form. The flexible graphitematerial is sometimes referred to as vermiculated graphite. Vermiculatedgraphite material is a material that has already been subjected to anexpansion process where typically the graphite material is treated withan acid and then subjected to a heat shock treatment.

[0056] The process then flows to block 604 where the graphite powderobtained from grinding the flexible graphite is then mixed with a resin.In one embodiment according to the present invention, the resin includesa phenolic resin that may be Borden Durite RD 2414, but the presentinvention may be equally practiced in connection with other resins. Thegraphite powder is mixed in an amount ranging between approximately10% - 90% by weight with phenolic resin in an amount ranging between10% - 90% by weight such that the sum of the x% graphite and y% phenolicresin, of the combination, equals 100%. Table 1 shows possible mixtureratios between graphite and resin and the corresponding resistivities ofthe mixtures in microhms per meter square. TABLE 1 Graphite ResinResistivity 90% 10%  17.8 Microhms/meter square 80% 20%  26.5Microhms/meter square 70% 30%  33.0 Microhms/meter square 60% 40%  61.1Microhms/meter square 50% 50%  90.2 Microhms/meter square 40% 60%  166.0Microhms/meter square 30% 70%  328.0 Microhms/meter square 20% 80%2294.0 Microhms/meter square 10% 90% N/A

[0057] Next, at block 608 the graphite powder mixed with the phenolicresin (mixture) is hot pressed. Before hot pressing, the combination ofgraphite powder with phenolic resin is introduced into a first mold. Themold may have an approximate dimension of 6″×9″×0.125″, but theembodiment of the process described herein may be equally practiced inconnection with molds having higher or lower dimensions. The mixturecombination is introduced into the first mold by pouring graphite powderand the phenolic resin into the first mold. The mixture is hot-pressedat a pressure less than 1 pound per square inch (psi) at approximately250° F. for approximately 30 minutes. As a result of subjecting themixture to hot pressing, the particles of the graphite powder and thephenolic resin bind together at a density of approximately 0.1 g/cc.However, this density may be different than 0.1 g/cc. The mixture isthen removed from the first mold and is placed into a second mold andhot-pressed at approximately 350° F. at 2000 psi, for approximately 30minutes.

[0058] The resulting graphite material obtained by way of the processdescribed above has a density of approximately 1.5 g/cm³. As one may seefrom Table 1, the more graphite the mixture has, the resulting graphitematerial's resistivity is lower, reaching 17.8 microhm per meter squarefor 90% graphite and 10% resin.

[0059]FIG. 7 illustrates a flow chart diagram in connection with afourth embodiment of a process of making a graphite material accordingto the present invention. Initially, at block 702, flexible graphite isground into a powder that has a particle size in a range ofapproximately 25 to 80 mesh. More details related to this process stepwere provided above in the description connected to the previousembodiment illustrated in FIG. 6. Next the process flows to step 704where the graphite powder is soaked in a cryogenic liquid. More detailwith respect to this step may be found above in the descriptionconnected to FIG. 1.

[0060] Next, at block 706 the soaked graphite is expanded. In oneembodiment according to the present invention, the soaked graphitecompound may be expanded by heating the soaked graphite compound to atemperature of approximately 650° F. One way to perform this expansionis by heating the soaked graphite as explained above in the descriptionconnected to FIGS. 1 and 2.

[0061] Next at step 708 the expanded graphite compound is mixed in anamount ranging between approximately 10% - 90% by weight with phenolicresin in an amount ranging between 10% -90% by weight. Table 2 belowillustrates possible mixtures of graphite with the resin and theirrespective resistivities. TABLE 2 Graphite Resin Resistivity 90% 10% 10.0 Microhms/meter square 80% 20%  17.0 Microhms/meter square 70% 30% 33.0 Microhms/meter square 60% 40%  38.7 Microhms/meter square 50% 50% 60.9 Microhms/meter square 40% 60%  84.5 Microhms/meter square 30% 70%134.0 Microhms/meter square 20% 80% 248.0 Microhms/meter square 10% 90%736.0 Microhms/meter square

[0062] Next the graphite mixture is hot pressed after initiallyintroducing the graphite mixture into a first mold. Hot pressing isperformed in a manner as explained above in the description inconnection with the embodiment of the process illustrated in FIG. 6.

[0063]FIG. 8 illustrates a flow chart in connection with an embodimentof a fifth process of making a graphite material according to thepresent invention. The embodiment of this process starts at block 802where flexible graphite is ground into a powder that has a particle sizein a range of approximately 25 - 80 mesh. Next the process flows toblock 804 where the graphite powder is soaked in a cryogenic liquid. Theprocess then flows to block 806 where the soaked graphite powder isexpanded by heating to a temperature at which the soaked graphite powderexpands. In one embodiment this temperature is approximately 650° F.,but the present invention equally applies in connection with heating atother temperatures that cause expansion of the soaked graphite flakes.Next at block 808, the expanded graphite powder is ground into a finergraphite powder that has a particle size in a range of approximately48 - 100 mesh but the present invention is not limited in scope to thisparticle size range. At block 810, the finer graphite powder is mixed inan amount ranging between approximately 10% - 90% graphite powder byweight with phenolic resin in amount ranging between 10% - 90% byweight. Next at block 812, the graphite mixture is hot pressed asexplained above in the description of the embodiments of the processesillustrated in FIGS. 6 and 7.

[0064] Table 3 illustrates possible mixture ratios between graphite andresin and the corresponding resistivities of the resulting graphitematerials. TABLE 3 Graphite Resin Resistivity 90% 10%  15.0Microhms/meter square 80% 20%  23.6 Microhms/meter square 70% 30%  25.8Microhms/meter square 60% 40%  46.1 Microhms/meter square 50% 50%  116.9Microhms/meter square 40% 60%  161.8 Microhms/meter square 30% 70% 186.8 Microhms/meter square 20% 80% 1219.9 Microhms/meter square 10%90% N/A

[0065]FIG. 9 illustrates a sixth embodiment of a process of making agraphite material according to the present invention. At block 902natural graphite flakes are soaked in an acid. In one embodiment theacid may be nitric acid or sulfuric acid. Next the process flows toblock 904 where the soaked natural graphite flakes are expanded. Theexpansion is performed by heating the soaked natural graphite flakes ata temperature of approximately 1200° F. to expand in a range of 200 -400 times depending on the graphite. Next, at block 906, the expandedsoaked natural graphite flakes are precompacted to a density ofapproximately 0.1 g/cm³. Next, at step 908 the expanded precompactedsoaked natural graphite flakes are ground to a particle size in anapproximate range of 25 - 80 mesh. At block 910, the graphite powder ismixed in a ratio ranging between approximately 10% - 90% graphite powderby weight with a phenolic resin in an amount ranging between 10% - 90%by weight. Next at block 912, the mixture is hot pressed. The stepsperformed during the hot press stage are similar to the steps describedabove in connection with hot pressing.

[0066] Table 4 illustrates possible combination ratios between graphiteand resin, and the corresponding resistivity of the resulting graphitematerials. TABLE 4 Graphite Resin Resistivity 90% 10%  18.05Microhms/meter square 80% 20%  21.3 Microhms/meter square 70% 30%  32.2Microhms/meter square 60% 40%  73.0 Microhms/meter square 50% 50%  83.0Microhms/meter square 40% 60%  119.0 Microhms/meter square 30% 70%4136.0 Microhms/meter square 20% 80% N/A 10% 90% N/A

[0067]FIG. 10 illustrates four graphs in connection with the resistivityof the graphite materials obtained by way of the four processesexplained in connection with FIGS. 6 - 9. The Y-axis indicates theresistivity in microhms per meter square. The X-axis indicates the ratioof graphite to resin utilized. The four different graphs illustrated inthe figure are distinguished from one another by the symbols shown inthe legend. For example, the graph designated by the symbol “X” is inconnection with the embodiment of the process explained in connectionwith FIG. 7. For this process, the resulting graphite material has aresisitivity of approximately 10 microhms per meter square for acombination of 90% graphite and 10% phenolic resin.

[0068] The graph designated by the symbol “▪” is in connection with theembodiment of the process explained in connection with FIG. 8. Theresulting graphite material obtained by way of this process has aresistivity of approximately 16 microns per meter square, for a ratio of90% graphite and 10% phenolic resin. Note that for combinations in theranges of approximately 90%/10% - 75%/25% and 65%/35% - 40%/60% ofgraphite-to-phenolic resin, the graphite material obtained by way of theprocess represented by graph X has the lowest resistivity, compared withthe resistivities of the other graphite materials, obtained by way ofthe other three processes.

[0069] In the foregoing specification, the invention has been describedwith reference to specific embodiments thereof. It will however beevident that various modifications and changes can be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is:
 1. A method of making a graphite material comprisingthe steps of: a) grinding flexible graphite into a powder having aparticle size in a range of 25 to 80 mesh; b) mixing the graphite powderin an amount ranging between approximately 10% - 90% by weight, with aresin, in an amount ranging between approximately 10% - 90% by weight;and c) hot pressing said graphite powder mixed with said resin.
 2. Themethod of claim 1 wherein before hot pressing, said graphite powdermixed with said resin is introduced into a first mold.
 3. The method ofclaim 2 , said hot pressing is performed at a pressure that is less than1 pounds per square inch (psi) and at a temperature of approximately230° Fahrenheit.
 4. The method of claim 3 wherein hot pressing furtherincluding, removing from said first mold said graphite powder mixed withthe resin, placing said graphite powder mixed with the resin into asecond mold, and hot-pressing said graphite powder mixed with the resinat approximately 2000 pound per square inch (psi) and approximately 350°F. for approximately 30 minutes.
 5. The method of claim 1 wherein saidgraphite material has a density of approximately 1.5 grams/centimetercube (g/cc).
 6. The method of claim 1 wherein said resin includesphenolic resin.
 7. The method of claim 1 wherein said flexible graphiteincludes recycled graphite foil.
 8. The method of claim 3 whereinhot-pressing the graphite powder mixed with the resin at a pressure thatis less than 1 pound per square inch (psi) and at a temperature of 230°F. is performed for approximately 30 minutes.
 9. A method of making agraphite material, the method comprising: a) grinding flexible graphiteinto a powder having a particle size in a range of approximately 25 to80 mesh; b) soaking the graphite powder in a cryogenic liquid; c)expanding the soaked graphite powder; d) mixing the graphite powder inan amount ranging between approximately 10% - 90% by weight, with aresin, in an amount ranging between approximately 10% - 90% by weight;and e) hot pressing said graphite powder mixed with said resin.
 10. Themethod of claim 9 wherein before hot pressing, said graphite powdermixed with said resin is introduced into a first mold.
 11. The method ofclaim 10 , said hot pressing is performed a pressure that is less than 1pound per square inch (psi) and at a temperature of approximately 230°Fahrenheit.
 12. The method of claim 11 wherein said hot pressing furtherincluding, removing from said first mold said expanded soaked graphitepowder mixed with the resin, introducing said expanded soaked graphitepowder mixed with the resin into a second mold, and hot-pressing saidexpanded soaked graphite powder mixed with the resin at approximately2000 pounds per square inch (psi) approximately 350° Fahrenheit forapproximately 30 minutes.
 13. The method of claim 9 wherein saidgraphite material has a density of approximately 1.5 grams/centimetercube (g/cc).
 14. The method of claim 9 wherein said resin includesphenolic resin.
 15. The method of claim 9 wherein said flexible graphiteincludes recycled graphite foil.
 16. The method of claim 11 whereinhot-pressing the graphite powder mixed with the resin at a pressure thatis less than 1 pound per square inch (psi) and at a temperature ofapproximately 230° Fahrenheit is performed for approximately 30 minutes.17. The method of claim 9 , wherein expanding the soaked graphite powderis performed by heating the expanded graphite powder to a temperature ofapproximately 650° Fahrenheit (F.).
 18. A method of making a graphitematerial, the method comprising: a) grinding flexible graphite into apowder having a particle size in a range of approximately 25 to 80 mesh;b) soaking the graphite powder in a cryogenic liquid; c) expanding thesoaked graphite powder; d) grinding the expanded soaked graphite powderinto a powder having a particle size in a range of approximately 48 to100 mesh; e) mixing the graphite powder in an amount ranging betweenapproximately 10% - 90% by weight, with a resin, in an amount rangingbetween approximately 10% - 90% by weight; and f) hot pressing saidgraphite powder mixed with said resin.
 19. The method of claim 18wherein before hot pressing, said graphite powder mixed with said resinis introduced into a first mold.
 20. The method of claim 19 , said hotpressing is performed at a pressure that is less than 1 pound per squareinch (psi) and at a temperature of approximately 230° Fahrenheit. 21.The method of claim 20 wherein said hot pressing further including,removing from said first mold said graphite powder mixed with the resin,introducing said graphite powder mixed with the resin into a secondmold; and hot-pressing said graphite powder mixed with the resin atapproximately 2000 pound per square inch (psi) and approximately 350°Fahrenheit for approximately 30 minutes.
 22. The method of claim 18wherein said graphite material has a density of approximately 1.5grams/centimeter cube (g/cc).
 23. The method of claim 18 wherein saidresin includes phenolic resin.
 24. The method of claim 18 wherein saidflexible graphite includes recycled graphite foil.
 25. The method ofclaim 20 wherein hot-pressing the graphite powder mixed with the resinat a pressure that is less than 1 pound per square inch (psi) and at atemperature of approximately 230° Fahrenheit is performed forapproximately 30 minutes.
 26. The method of claim 18 , wherein expandingthe soaked graphite powder is performed by heating the expanded graphitepowder to a temperature of approximately 650° Fahrenheit (F.).
 27. Amethod of making a graphite material, the method comprising: a) soakinggraphite flakes into an acid; b) expanding the soaked graphite flakes;c) precompacting the expanded soaked graphite flakes; d) grinding theprecompacted expanded soaked graphite flakes into a powder having aparticle size in a range of approximately 25 to 80 mesh; e) mixing theground, precompacted expanded soaked graphite powder in an amountranging between approximately 10% - 90% by weight, with a resin, in anamount ranging between approximately 10% - 90% by weight; and f) hotpressing said ground, precompacted expanded graphite powder mixed withsaid resin.
 28. The method of claim 27 , wherein before hot pressing,said graphite powder mixed with said resin is introduced into a firstmold.
 29. The method of claim 28 , said hot pressing is performed at apressure that is less than 1 pound per square inch (psi) and at atemperature of approximately 230° Fahrenheit.
 30. The method of claim 29wherein said hot pressing further including, removing from said firstmold said graphite powder mixed with the resin, placing said expandedsoaked graphite powder mixed with the resin into a second mold; andhot-pressing said graphite powder mixed with the resin at approximately2000 pounds per square inch (psi) and approximately 350° Fahrenheit forapproximately 30 minutes.
 31. The method of claim 27 wherein saidgraphite material has a density of approximately 1.5 grams/centimetercube (g/cc).
 32. The method of claim 27 wherein said resin includesphenolic resin.
 33. The method of claim 29 wherein hot-pressing thegraphite powder mixed with the resin at less than 1 pound per squareinch (psi) and at approximately 250° F. is performed for approximately30 minutes.
 34. The method of claim 27 , said acid includes sulfuricacid.
 35. The method of claim 27 , said acid includes nitric acid. 36.The method of claim 29 wherein hot-pressing the graphite powder mixedwith the resin at a pressure that is less than 1 pound per square inch(psi) and at a temperature of approximately 230° Fahrenheit is performedfor approximately 30 minutes.
 37. A graphite material made by a processcomprising: a) grinding flexible graphite into a powder having aparticle size in a range of 25 to 80 mesh; b) mixing the graphite powderin an amount ranging between approximately 10% - 90% by weight, with aresin, in an amount ranging between approximately 10% - 90% by weight;and c) hot pressing said graphite powder mixed with said resin.
 38. Thegraphite material of claim 37 wherein before hot pressing, said graphitepowder mixed with said resin is introduced into a first mold.
 39. Thegraphite material of claim 38 , said hot pressing is performed at apressure that is less than 1 pound per square inch (psi) and at atemperature of approximately 230° Fahrenheit.
 40. The graphite materialof claim 39 wherein said hot pressing further including, removing fromsaid first mold said graphite powder mixed with the resin, placing saidgraphite powder mixed with the resin into a second mold, andhot-pressing said graphite powder mixed with the resin at approximately2000 pounds per square inch (psi) and approximately 350° Fahrenheit forapproximately 30 minutes.
 41. The graphite material of claim 37 whereinsaid graphite material has a density of approximately 1.5grams/centimeter cube (g/cc).
 42. The graphite material of claim 37wherein said resin includes phenolic resin.
 43. The graphite material ofclaim 37 wherein said flexible graphite includes recycled graphite foil.44. The graphite material of claim 39 wherein hot-pressing the graphitepowder mixed with the resin at a pressure that is less than 1 pound persquare inch (psi) and at a temperature of approximately 230° Fahrenheitis performed for approximately 30 minutes.
 45. A graphite material madeby a process comprising: a) grinding flexible graphite into a powderhaving a particle size in a range of 25 to 80 mesh; b) soaking thegraphite powder in a cryogenic liquid; c) expanding the soaked graphitepowder; d) mixing the expanded soaked graphite powder in an amountranging between approximately 10% - 90% by weight, with a resin, in anamount ranging between approximately 10% - 90% by weight; and e) hotpressing said expanded soaked graphite powder mixed with said resin. 46.The graphite material of claim 45 wherein before hot pressing, saidexpanded soaked graphite powder mixed with said resin is introduced intoa first mold.
 47. The graphite material of claim 46 , said hot pressingis performed at a pressure that is less than 1 pound per square inch(psi) and at a temperature of approximately 230° Fahrenheit.
 48. Thegraphite material of claim 47 wherein said hot pressing furtherincluding, removing from said first mold said expanded soaked graphitepowder mixed with the resin, placing said expanded soaked graphitepowder mixed with the resin into a second mold, and hot-pressing saidexpanded soaked graphite powder mixed with the resin at approximately2000 pounds per square inch (psi), and approximately 350° Fahrenheit,for approximately 30 minutes.
 49. The graphite material of claim 45wherein said graphite material has a density of approximately 1.5grams/centimeter cube (g/cc).
 50. The graphite material of claim 45wherein said resin includes phenolic resin.
 51. The graphite material ofclaim 45 wherein said flexible graphite includes recycled graphite foil.52. The graphite material of claim 47 wherein hot-pressing the graphitepowder mixed with the resin at a pressure that is less than 1 pound persquare inch (psi) and at a temperature of approximately 230° Fahrenheitis performed for approximately 30 minutes.
 53. The graphite material ofclaim 45 , wherein expanding the soaked graphite powder is performed byheating the soaked graphite powder to a temperature of approximately650° Fahrenheit (F.).
 54. A graphite material made by a processcomprising: a) grinding flexible graphite into a powder having aparticle size in a range of 25 to 80 mesh; b) soaking the graphitepowder in a cryogenic liquid; c) expanding the soaked graphite powder;d) grinding the expanded soaked graphite powder into a powder having aparticle size in a range of approximately 48 to 100 mesh; e) mixing thegraphite powder in an amount ranging between approximately 10% - 90% byweight, with a resin, in an amount ranging between approximately 10% -90% by weight; and f) hot pressing said graphite powder mixed with saidresin.
 55. The graphite material of claim 54 wherein before hotpressing, said graphite powder mixed with said resin is introduced intoa first mold.
 56. The graphite material of claim 55 , said hot pressingis performed at less than 1 pound per square inch (psi) and atapproximately 250° F.
 57. The graphite material of claim 56 whereinhot-pressing the graphite powder mixed with the resin at a pressure thatis less than 1 pound per square inch (psi) and at a temperature ofapproximately 230° Fahrenheit is performed for approximately 30 minutes.58. The graphite material of claim 57 wherein said hot pressing furtherincluding, removing from said first mold said graphite powder mixed withthe resin, placing said graphite powder mixed with the resin into asecond mold, and hot-pressing said graphite powder mixed with the resinat approximately 2000 pounds per square inch (psi) and approximately350° Fahrenheit for approximately 30 minutes.
 59. The graphite materialof claim 54 , wherein expanding the soaked graphite powder is performedby heating the expanded graphite powder to a temperature ofapproximately 650° Fahrenheit (F.).
 60. A graphite material made by aprocess comprising: a) soaking graphite flakes into an acid; b)expanding the soaked graphite flakes; c) precompacting the expandedsoaked graphite flakes; d) grinding the precompacted expanded soakedgraphite into a powder having a particle size in an approximate range of25 to 80 mesh; e) mixing the expanded soaked graphite powder in anamount ranging between approximately 10% - 90% by weight, with a resin,in an amount ranging between approximately 10% - 90% by weight; and f)hot pressing said graphite powder mixed with said resin.
 61. Thegraphite material of claim 60 wherein before hot pressing, said graphitepowder mixed with said resin is introduced into a first mold.
 62. Thegraphite material of claim 61 , said hot pressing is performed at apressure that is less than 1 pound per square inch (psi) and at atemperature of approximately 230° Fahrenheit.
 63. The graphite materialof claim 62 wherein said hot pressing further including, removing fromsaid first mold said graphite powder mixed with the resin, placing saidgraphite powder mixed with the resin into a second mold, andhot-pressing said graphite powder mixed with the resin at approximately2000 pounds per square inch (psi) and approximately 350° Fahrenheit forapproximately 30 minutes.
 64. The graphite material of claim 62 whereinhot-pressing the graphite powder mixed with the resin at a pressure thatis less than 1 pound per square inch (psi) and at a temperature ofapproximately 230° Fahrenheit is performed for approximately 30 minutes.65. The graphite material of claim 60 wherein expanded soaked graphiteflakes are precompacted to a density of approximately 0.1 g/cc.
 66. Agraphite material made by a process comprising: a) grinding flexiblegraphite into a powder; b) mixing the graphite powder with athermoplastic material; and c) injecting into a mold the graphite powdermixed with the thermoplastic material.
 67. The graphite material ofclaim 66 wherein said plastic material formed has a density ofapproximately 1.7 grams/centimeter cube.
 68. The process of claim 66wherein said thermoplastic material is Poly Phelene Sulfide.
 69. Abipolar plate made of the graphite material of claim 67 .
 70. A gasketmade by the graphite material of claim 67 .
 71. A graphite material madeby a process comprising: a) grinding flexible graphite into a graphitepowder; b) soaking said graphite powder into a cryogenic liquid; c)expanding the soaked braphite powder; d) mixing the expanded graphitewith a thermoset resin, and e) heating the graphite resin mixture underpressure. f) heat treating the product of step e.
 72. The graphitematerial of claim 71 wherein expanding the soaked graphite powder isperformed by heating the soaked graphite material.
 73. The graphitematerial of claim 71 wherein said graphite of step a is flexiblegraphite foil.
 74. The graphite material of claim 71 wherein saidgraphite foil is recycled graphite foil.